There’s a very fine and almost invisible line between support and trending on social media. When tragic events like Friday's terrorist attacks in Paris unfold, marketers face a challenge: Should they show their support for victims on social media, and if so, how do they do so in an authentic way?

This weekend, many major brands—including Amazon, Google and Uber—swiftly took to Twitter, Instagram, Facebook and other platforms to show their solidarity with France, often using the #PrayforParis hashtag. The rush to join the discussion didn't sit well with some consumers:

Still, Steven Heller, author of a number of books on design, told Fast Company that sharing supportive images is important: "We need symbols to express what [we] cannot say." They also offer brands a subtle way to join the conversation—to say something without sounding off. While many companies used the viral "Peace for Paris" sketch, others created their own images.

Uber, for example, added the image of the French flag to the cars in its app:

Amazon had its own spin, putting the flag front and center on its homepage:

Airbnb, like many companies, made the French flag part of its logo while also offering help to those stranded in Paris:

Google, Skype, Verizon and Sprint all made international calls free for consumers: